Production of diolefins



Feb. 18, 1947. w, D, SEYFRED 2,416,227

PRODUCTION OF DIOLE FINS Filed lay 18, 1944 Wator Quench T I QuenchTower WNVENTOR.

ATTORNEY.

Patented Feb. 18, 1947 UNITED STATES PATENT OFFICE.

PRODUCTION OF DIOLEFINS Wilson D. Seyfried, Wooster, Ten, assignor toStandard Oil Development Company, a corporation of Delaware ApplicationMay 18, 1944, Serial No. 536,210

4 Claims.

ducing diolefins of the character of butadieneincludes the steps ofsubjecting a predominantly olefinic feed stock to dehydrogenationconditions in a dehydrogenation reactor to form diolefins'as well asunsaturated materials, such as acetylencs. The hydrocarbon stream fromthe dehydrogenation unit is quenched by being brought into intimatecontact with a quench oil, and after this quenching step it is furthercooled to condense a diolefin-containing fraction which is removed to asuitable stabilization zone. The step in the process of contacting thehydrocarbon fraction removed from the dehydrogenation reactor with aquench oil is essential for profitable commercial operations in order toterminate the reaction and prevent the conversion of diolefins into lessdesirable materials. The quenching step is necessarily carried out atrelatively high temperatures, and if free oxygen is allowed to enter thequenching zone it will react with the unsaturated materials presenttherein to form peroxides. Such peroxides are to be avoided because theynot only are easily detonated, but in addition they catalyze theformation of high molecular weight polymers from the unsaturatedhydrocarbons, such as diolefins and acetylenes, present in thehydrocarbon stream.

The product removed from the dehydrogenation reaction does not have freeoxygen present therein, so the quenching zone may be maintainedoxygen-free by the use of suitable quenching oil. This may convenientlybe accomplished by employing initially as a quenching oil an oilpreviously treated to remove dissolved oxygen therefrom and preventingthe contact between the 011 and air or oxygen-containing gas while it isbeing utilized in the system.

A preferred embodiment of the present invention will now be described inconjunction with the drawing, in which the sole figure is in the form ofa diagrammatic fiow sheet.

Turningnow specifically to the drawing, an

olefin-containing feed stock is passed via inlet ll into dehydrogenationreactor I2, maintained under suitable conditions to cause the conversionof substantial amounts of the olefins in the feed stock to diolefins. Inaddition to the resulting diolefins, minor amounts of acetylenes arealso formed in the dehydrogenation reactor. Hot hydrocarbon product isremoved from vessel l2'by .line l3, having cooler l4 present therein.The

vapors removed from cooler I4 are still at a relatively high temperatureand will cause the conversion of the desirable diolefins intoundesirable materials if the temperature thereof is not reduced rapidly,and for this reason the vapors are discharged from line l3 into vesselI5, which serves as a quenching zone. Into an upper portion of tower I5an oxygen-free heavy quench oil is introduced through inlet l6 and flowsdownwardly through the tower countercurrent to the hot hydrocarbonvapors let into the tower through line l3. The contacting of the hotvapors with the quenching oil should be under such conditions that thetemperature of .the hot vapors is reduced several hundred degrees F. ina very short interval of time. This quenching must be sufiicient toreduce the temperature of the vapor below that at which substantialconversion of the diolefins into other products will take place. Thequenched vapors are withdrawn from tower l5 through line H and subjectedto cooling steps to cause cooling and condensation of the desireddiolefln-containing product. In the drawing the hot vapors pass throughlinesll into cooler l8 of the heat exchanger type and pass thencethrough line l9 into tower 20, where they are quenched by contact withwater. Quenching water accumulating in the lower portion of the tower iswithdrawn through line 2| containing pump 22 and cooling means 23 andrecycled back to the tower, being discharged into the upper portionthereof. The hot vapors fiow upwardly through trained water from thehydrocarbon vapors.

Separated water is removed from the lower portion of the drum throughoutlet 26 and hydrocarbon vapors from the upper portion of the drumthrough outlet 21 and passed through compressor 28, cooler 29 and asecond drum 30. The compression and cooling steps to which the vaporsare subjected causes the condensation of the major portion of thediolefin fraction. This desired fraction settles out in drum 30 and maybe solved therein may be removed from the lower portion of the tower vialine 35 and hydrocarbon gases and vapors are removed from the top of thetower by line 36 and discarded from the system.

A high boiling oil suitable for use in the quenching zone I is passedthrough inlet 40 and to still 4| provided with a suitablepressurereducing means 42 and a heating means 43. The heavy oil isrefluxed under reduced pressure in the still 'to remove therefromsubstantially all of the dissolved oxygen therein. The oxygenfree heavyoil is removed from still 4| through line 44 and passed into storagetank 45. Contact with oxygen in tank 45 is prevented by blanketin'g thesurface of the oil with an oxygenfree gas. A suitable inert gas for thispurpose has been found to be methane, but other oxygenfree gases, suchas flue gas or nitrogen, may also be used for this purpose. The inertgas may be 'stored in vessel 46 and removed therefrom to the upperportion of tank 45 by line 41 controlled by valve 48 in order tomaintain an oxyp gen-free gas blanketover the quench oil at all times.As oil is needed for the quenching tower l5, it is withdrawn from tank45 by line 49 controlled by valve 50 and allowed to enter the tower viainlet l6.

The quenching oil accumulated at the bottom of tower l5 has dissolvedtherein small amounts of the hydrocarbon vapors. This accumulated quenchoil is withdrawn from the tower through line 58 containing pump 52 andthe stream split, with a portion being returned to the tower by line 53and the remainder being passed through line 54 to a stripping tower 55provided with heating means 55. Vapors separated from the quenching oilin stripping tower 55 are returned to quenching tower l5 through line51. The stripped quenching oil resulting from the stripping action intower 55 is withdrawn from the bottom of the tower through line 34,passed through a cooler 58 and is then used as the lean absorbent oil inabsorption tower 33. The rich absorption oil removed from tower 33 vialine 35 is admixed with the oil flowing in line 53 and the mixturereturned to quenching tower l5.

As a specific example of the preparation of the quench oil, a Coastalgas oil having an initial boiling point of 590 F., a final boilingpointof 720 F., a viscosity at 100 F. of 77.9 Saybolt seconds, and agravity of 25.7" A. P. I. was refluxed in a still maintained under apressure ranging from 2 to 3 mm. absolute until substantially all of thedissolved oxygen originally present in the oil was removed therefrom.This oil was then stored under a blanket of methane in a storage tankand a quench oil was withdrawn therefrom as desired for quenching thehot va pors removed from a. dehydrogenation reactor. The substitution ofthis oxygen-free quench oil for the quench oil previously employedresulted in a substantial reduction in the polymers formed in thehydrocarbon stream and reduced substantially the fouling of theequipment. As another specific example, a raflinate having an initialboiling point "of"590'F. and a final boiling point of 720 F., and freedfrom oxygen by refluxing under vacuum, has been employed as a quenchoil.

The temperatures of the dehydrogenation reaction and the suitablequenching range for reducing the temperatures of the gaseous productremoved from the dehydrogenation reactorcare well known to the art andare described, for example, in detail in U. S. patent application SerialNo. 510,204, filed in the name of Carl E. Kleiber et al. on November 13,1943. As a typical example, it may be stated that the hydrocar-- stoodthat. these conditions are given by way of example only, and are notintended as limitations of the process.

Having fully described and illustrated the practice of the presentinvention, what I desire to claim is: 1

1. In a process for treating hydrocarbons including the steps of passingan olefin-containing hydrocarbon feed stock into a dehydrogenation zoneand maintaining it in said zone under conditions to cause the. formationof diolefin and acetylene, passing the product through a quenching zone,removing the product from the quenchmg zone, further cooling it tocondense at least a portion of the hydrocarbons, separating thecondensed hydrocarbons and passing uncondensed hydrocarbons into anabsorption zone,

the steps of stripping a heavy mineral oil under conditions of elevatedtemperature to remove dissolved oxygen therefrom, contacting thedehydrogenated product in the quenching zone with said oxygen-freemineral oil, and contacting the uncondensed hydrocarbons in theabsorption zone with said oxygen-free mineral oil.

2. In the treatment of a, hydrocarbon feed stock containing olefins bypassing the feed stock the quenching oil in the quenching zone and asthe absorption oil in the absorption zone.

3. A process in accordance with claim 2 in which the heavy oil is a,naphthenic gas oil boiling within the rangeof 590 to 720 F.

5 e 4. A method in accordance with claim 2 in which the heavy oil is araflinate boiling in the FOREIGN PATENTS range to Number Country DateWILSON B E F a 463,244 British Mar. 24, 1937 REFERENCES CITED 0 OTHERREFERENCES The following references are of reccrd in the Scott, Jour.Ind. Eng. Chem, News ed., vol. file of this patent: 18, 404 (1940).(Patent Office Library.)

Pittsburgh, etc., Research Bulletin No. 7381-3,

UNHED STATES PATENIS The Storage of Butadiene, pp. 26 and a1 (1942).

Number Name Date 2,209,215 Wiezevich et a1 July 23, 1940 2,378,067Dorset et a1 June 12, 1945

